1. Field of the Invention
The present invention relates to an attraction type magnetic levitating apparatus for supporting and guiding a levitated object by utilizing magnetic attraction and, more particularly, to an attraction type magnetic levitating apparatus wherein the number of electromagnets required to support and guide a levitated object is decreased to reduce the apparatus in size and weight.
2. Description of the Related Art
Recently, as a part of office automation, a transportation unit is used to move slips, documents, cash, data files, and the like between a plurality of points in a building.
A transportation unit used for such a purpose is required to have a function for quickly and quietly moving an object to be transported. Therefore, according to some transportation units of this type, a transportation vehicle is supported on a guide rail in a noncontact state, and is caused to travel in this state. Of such transportation units, a unit which uses an attraction type magnetic levitating apparatus for magnetically supporting a transportation vehicle as a levitated object in a noncontact state is excellent in tracking characteristics and in prevention of noise and dust.
When a levitated object is to be supported by using an attraction type magnetic levitating apparatus, it is important how to suppress rolling and yawing of the levitated object and to maintain a magnetically stable levitated state when the levitated object receives a lateral external force, i.e., an external force in a guiding direction perpendicular to a levitating direction while, e.g., the object passes through a curved portion of a guide rail.
For this reason, in a conventional attraction type magnetic levitating apparatus such as disclosed in "Int. Conf. on MAGLEV & LINEAR DRIVES", May 14-16, 1986, VANCOUVER, B.C., CANADA, a guiding electromagnet is arranged in addition to a levitating electromagnet arranged to oppose a guide rail. This guiding electromagnet is controlled to obtain a required guiding force. According to another conventional apparatus, two electromagnets are arranged at each support point such that these electromagnets are located on both the sides of a guide rail so as to be offset from each other, and are controlled, thereby obtaining supporting and guiding forces without interference between these forces.
The conventional attraction type magnetic levitating apparatus having the above-described arrangement, however, poses the following problem. Since the levitating direction control and the guiding direction control of the levitated object are independently performed, the number of electromagnets is doubled as compared with a case where no guide control is performed, i.e., a large number of electromagnets are required. For this reason, a magnetic support unit constituted by the electromagnets and the levitated object itself are increased in size as well as weight. As a result, a structure, such as guide rails, for supporting the levitated object from the ground must be strengthened in accordance with the increase in weight to be supported, resulting in an increase in size of the overall apparatus.
As described above, in the conventional attraction type magnetic levitating apparatus, since attraction control in the supporting direction and that in the guiding direction are independently performed, the size of the apparatus is increased due to an increase in size and weight of the magnetic support unit and the levitated object itself.